The prior art already discloses radiation sensor means which are used e.g. for detecting a quantum radiation. A disadvantage of such sensors is that special problems arise in connection with the detection of radiations occurring comparatively rarely and as punctiform radiation. Due to the low occurrence probability, a large sensor surface is necessary so as to be able to detect the events. On the other hand, the punctiform event is averaged by the large surface, the sensors lose sensitivity and the signal-to-noise ratio deteriorates.
This problem can be solved by using a plurality of individual elements which are arranged in a matrix.
However, also this type of arrangement of the individual elements in a matrix entails essential problems. These problems arise when the matrix elements are read, which detect the punctiform radiation occurring with little probability. Due to so-called systematic addressing, a complete addressing cycle of the whole matrix is required in each individual case. The result obtained is the address as well as the value of the active matrix element, which is normally referred to as pixel.
A special disadvantage arises in cases of use where only the events are detected, i.e. where it is only detected how often radiation falls on the sensor. In this case, a very high percentage of the information supplied by this kind of addressing cannot be utilized.
A further problem arising in connection with these cases of use is that the reaction velocity of individual sensor elements may exceed by far the system clock for the whole sensor element matrix. Reaction velocity means, in this connection, the velocity with which the charge carriers generated by the incident radiation are decomposed in the radiation sensor element. This decomposition is normally referred to as recombination. A problem arises in the case of a renewed pass of the system clock, if the reaction time of the sensor, which is determined by the reaction velocity, has not yet elapsed after a previous incidence of radiation. In this case, the sensor will output a signal with regard to which it is not known whether it has been generated by new radiation falling on the sensor or by not yet fully recombined charge carriers.
DE-4224358 C1 describes a radiation sensor means having a high sensitvity and a high dynamic range and serving to detect quantum radiation. When such a known radiation sensor means is used for detecting how often a radiation falls on said sensor, the above described problems with regard to the reaction velocity and with regard to the system clock arise when said radiation sensor means are read.
DE 41 18 154 A1 describes an array comprising a sensor matrix and a reset arrangement. This known array comprises a plurality of sensors which are arranged in a matrix and which are sensitive to light and X-rays, respectively, said sensors generating charges in response to the incident amount of radiation. Each of the sensors comprises an electric switch. The arrangement is provided with a switching line for each line of sensors, which is adapted to be used for activating the individual switches so that the charges generated will flow off through associated read-out lines. For eliminating residual charges after a read-out operation, the array comprises a reset arrangement activating the sensors after the read-out operation via the read-out line thereof, whereby the electric switches of the sensors are rendered conducting and the residual charges, which are stored in the sensors after the previous read-out operation, flow off via the associated read-out lines. After a predetermined number of clocks of a reset clock, the respective read-out lines are deactivated again.